Multiple carrier mobile communication systems are configured on the basis of transmitters and receivers capable of transmitting and receiving multiple carrier data signals. One example of a multiple carrier radio transmission system is Orthogonal Frequency Division Multiplexing (OFDM) in which an OFDM transmitter broadcasts information consisting of symbols containing a plurality of equally spaced carrier frequencies. The characteristics of the wireless communication channel typically vary over time due to changes in the transmission path. For demodulating OFDM modulated data in the presence of substantial time variations of the transmission channel, knowledge of the transmission channel frequency response is required. This necessitates that the receiver provides an appropriate channel estimate of the transmission channel.
A transmission channel is known to be characterized among a number of parameters by a quantity known as the Doppler spread of the channel. When a user or reflector in its environment is moving, the user's velocity causes a shift in the frequency of the signal transmitted along each signal path. This phenomenon is known as the Doppler shift. Signals travelling along different paths can have different Doppler shifts, corresponding to different rates of change in phase. The difference in Doppler shifts between different signal components contributing to a single fading channel tap is known as the Doppler spread. Doppler spread estimation is crucial to channel estimation and to any other block in the system which requires an indication of the speed of the mobile, e.g. whether it is static or not, to perform some specific signal processing.